Use of the hierarchical modulation scheme is known as one of answers to perform efficient data mapping to wireless channel resources in the field of wireless communication techniques. The hierarchical modulation scheme is becoming an interesting object in researches in both the scientific field and the industrial field.
The hierarchical modulation scheme is one of techniques which modulates (multiplex-modulates) collectively information in plural channels destined for plural user terminals, and can set grades (hierarchy) of communication quality to the plural channels to be multiplex-modulated.
For example, in the hierarchical modulation scheme, bit positions having different degrees of the quality (degree of susceptibility to error) is raised in a bit string, associated with a signal point (constellation point) arranged on a phase plane, due to the association. The bit positions of information bits to be associated with a signal point are controlled according to importance or priority of the information, thereby to offer different levels of resistance to reception error to different services and users. One of purposes of using such the hierarchical modulation scheme is to increase the whole system capacity according to channel conditions or service modes.
Further, it is tried to introduce the hierarchical modulation scheme into Digital Video Broadcast (DVB) standard, for example. Concept of the hierarchical modulation scheme in DVB is to change the modulation order. For example, a higher modulation order is assigned to a receiver closer to the transmitter, while a low modulation order is assigned to a receiver farther from the transmitter.
In interesting researches relating to portable image transmission systems, use of the hierarchical modulation scheme realizes high-quality and high-speed digital image transmission in a fading channel whose bandwidth is limited. This scheme uses hierarchical Quadrature Amplitude Modulation (QAM) to offer non-uniform transmission reliability according to a layer of a compressed image by Adaptive Discrete Cosine Transform (ADCT) which is general in the image transmission. As a result, this makes it possible to improve the performance of Signal to Noise Ratio (SNR) of rearranged images. There is also proposed a hierarchical modulation scheme with power allocation in Orthogonal Frequency Division Multiplexing Access (OFDMA). Whereby, the number of independent links can be increased and a large capacity can be realized.
Further, it is proposed to realize the system capacity and improve the system fairness with use of multiple best user scheduling in Code Division Multiple Access (CDMA) based on multi-code. The hierarchical modulation scheme is likely to be beneficial to multiple best user opportunistic scheduling which adaptively distinguishes between the normal modulation scheme and the hierarchical modulation scheme.
In order to improve the performance (reception quality) of the fading channel, constellation is discussed along with (phase) rotating operation. According to this rotation mechanism, it is possible to increase Minimum Product Distance (MPD) rather than Minimum Euclidean Distance (MED) on the fading channel to realize so-called modulation diversity.    Non-Patent Document 1: M. Morimoto, M. Okada, and S. Komaki, “A hierarchical image transmission system in a fading channel”, in Proc. IEEE Int. Conf. Universal Personal Commun. (ICUPC '95), pp. 769-772, October 1995.    Non-Patent Document 2: S. Pietrzyk, and G. J. M. Janssen, “Subcarrier and power allocation for QoS-aware OFDMA system using embedded modulation”, in Proc. Int. Conf. Commun. (ICC), Vo. 6, pp. 3202-3206, 2004.    Non-Patent Document 3: P. K. Vitthaladevuni, and M-S. Alouini, “A recursive algorithm for the exact BER computation of generalized hierarchical QAM constellation”, IEEE Trans. On Information Theory, Vol. 49, No. 1, pp. 297-307, January 2003.    Non-Patent Document 4: 3GPP TR 25.814, Physical layer aspects for evolved UTRA, V7.0.0, P 22, June, 2006.    Non-Patent Document 5: K. Ramchandran, A. Orteg, K. M. Uz, and M. Vetterli, “Multiresolution broadcast for digital HDTV using joint source/channel coding”, IEEE J. Sel. Are as Commun., Vol 11, No. 1, pp. 6-22, January 1993.    Non-Patent Document 6: D. I. Kim, “Two-best user scheduling for high-speed downlink multicode CDMA with code constraint”, in Proc. IEEE Conf. Global Commun. (Globecomm), pp. 2659-2663, Nov. 29-Dec. 3, 2004.    Non-Patent Document 7: M. J. Hossain, M-S. Alouini, and V. K. Bhargava, “Rate adaptive hierarchical modulation-assisted two-user opportunistic scheduling”, IEEE Trans. On Wireless Commun. Vol. 6, No. 6, pp. 2076-2085, June 2007.    Non-Patent Document 8: V. M. DaSilva, and E. S. Sousa, “Fading-resistant modulation using several transmitter antennas”, IEEE Transaction on Communications, Vol. 45, No. 10, pp. 1236-1244, October 1997.    Non-Patent Document 9: J. Boutros, E. Viterbo, C. Rastello, and J. C. Befiore, “Good lattice constellation for both Rayleigh fading and Gaussian channel”, IEEE trans. on information theory, Vol. 42, No. 2, pp. 502-518, March 1996.    Non-Patent Document 10: J. Boutros, E. Viterbo, “Signal space diversity: a power- and bandwidth-efficient diversity technique for the Rayleigh fading channel”, IEEE trans. on information theory, Vol. 44, No. 4, pp. 1453-1467, July 1998.